Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) are, either self-contained or in combination with Computed Tomography (CT) or Magnetic Resonance Imaging (MRI), two common techniques for imaging the human body or parts thereof. In particular, PET and SPECT allow imaging organs or metabolic processes in the human body and, e.g., determine therefrom the progress of a disease. For this, a patient is usually administered a radioactive tracer substance emitting particles, i.e. radiation, that can be captured and used as a basis for imaging. Further applications include preclinical studies, wherein small animals are imaged in order to determine the effects of new medication or treatment approaches. Also other imaging applications outside the field of medicine exist relying on the same principles.
For some applications, in particular medical applications, it can be advantageous to provide both, SPECT and PET, images of the same area of interest in a patient in order to exploit the advantages of both imaging modalities. Although making use of the same basic imaging approach (detecting gamma rays), the two most common imaging systems SPECT/CT and PET/CT, are currently, however, usually offered in different mechanical, frontend electronics and backend processing configurations. This leads to a more complicated supply chain for the different imaging systems and difficulties in the upgradability. Usually, PET and SPECT systems require different mechanical structures, different data acquisition paths and different photodetectors or combinations of photodetectors leading to little possible savings when combining the two imaging modalities in order to obtain a multimodal imaging device for providing images based on both imaging modalities.
In Mediso, “AnyScan: Triple Modality Molecular Imaging System”, product brochure, October 2011, there is introduced the AnyScan hybrid imaging system for early diagnosis and treatment for cancer, cardiac and neurological diseases. The presented device allows obtaining SPECT and PET images of a patient by means of a combined imaging system. The presented system comprises two separate imaging modalities, wherein each of the separate imaging modalities uses a separate gantry and separate electronics processors. The two devices can be mechanically coupled for obtaining PET and SPECT images of a patient.
One disadvantage of this solution, however, is that it requires two separate gantries, i.e. a rather complex and costly mechanical construction, and basically comprises two separate imaging devices placed side by side. Further, in order to obtain PET and SPECT images of one specific area of interest the patient has to be moved versus the two gantries because each of the two devices focuses a separate area of interest, which may lead to further difficulties if exact positioning or combination of the PET and SPECT information is required.
In U.S. Pat. No. 6,448,559 B1 a detector assembly for multi-modality scanners is disclosed. The assembly comprises a first layer for detecting low energy gamma radiation and X-rays and a second layer for detecting high energy gamma radiation. The first layer is generally transparent to high energy gamma radiation. The second layer may advantageously provide measurement of depth of interaction of the high energy radiation. The detector assembly is advantageously incorporated in a multi-modality PET/SPECT/CT scanner allowing simultaneous transmission and emission imaging with the same detection geometry.
In WO 02/079802 A2, systems and methods are described for a positron emission tomography camera with individually rotatable detector modules and/or individually movable detector modules. Further, a plurality of individually moveable shield sections are disclosed.
In US U.S. 2008/111081 A1 an imaging system and method for the non-pure Positron Emission Tomography are presented. The systen comprises a PET subsystem to detect the annihilated photons and a SPECT subsystem to detect the associated gamma. These two subsystems are connected by a triple coincidence circuit.